Magnetically driven antenna array



March 10, 1970 D. H. WE LLS 3,500,426

MAGNETICALLY DRIVEN ANTENNA ARRAY Filed June 5, 1966 3 Sheets-Sheet l INVENTOR. DONALD H. WELLS ym m ATTO R N EYS D. H. WELLS MAGNETICALLY DRIVEN ANTENNA ARRAY March 10, 1970 3 Sheets-Sheet 2 Filed June 5. 1966 INVENTOR. DONALD H. WELLS BY I ATTORNEYS March 10, 1970 D. H. WELLS MAGNETICALLY DRIVEN ANTENNA ARRAY 3 Sheets-Sheet 5 Filed June 5, 1966 INVENTOR. DONALD H. WELLS 2AM 204 I ATTORNEYS United States Patent 3,500,426 MAGNETICALLY DRIVEN ANTENNA ARRAY Donald H. Wells, Oregon, Ohio, assignor, by mesne as.- signments, to The Scott & Fetzer Company, Lakewood, Ohio, a corporation of Ohio Continuation-impart of application Ser. No. 500,931, Oct. '22, 1965. This application June 3, 1966, Ser.

Int. 01.11011 19/30 US. Cl. 343 s19 2 Claims ABSTRACT OF THE DISCLOSURE A magnetically driven antenna array in which all of the antenna dipole elements are parasitic. The array is driven by'an independent means consisting of a section of the transmitter source induces currents on the parasitic dipoles of the array, establishing a secondary or reradiated field. The total electromagnetic field in the vicinity of the array is a combination of the secondaryfields from transmission line. The incident plane wave of energy from all of the antenna elements and the incident field. In its simplest form, this field is a standing wave, whose vector H (magnetic lines of force) near the axis of the array where the driven element is placed, establishes a strong magnetic flux which links the loop formed by" the section of transmission line. The time varying flux drives the transmission line by inducing voltages and currents on it that can be conveniently fed to the associated receiver.

This is a continuation-in-part of application Ser. No. 500,931, now abandoned, filed'Oct. 22, 1965. i

SUMMARY OF THE INVENTION tween the antenna elements; lead coupling means on the inductance element; and means electrically coupled to. the lead coupling means for delivering a signal to a receiver, whereby the lead coupling means are'positioned on the inductance element at a point where the impedance of the inductance elements is substantially equal to the impedance of the means for deliivering the signal to the receiver. v

FIGURE 1 is a perspective view of an antenna system incorporating the principles of the present invention;

FIGURE 2 is an enlarged fragmentary view of the feed point and the inductance element;

FIGURES 3, 4, and 5 diagrammatically illustrate the current and magnetic field configuration established by the electromagnetic energy being recieved by the antenna system illustrated in FIGURES 1 and 2; I

FIGURES 6 through 9 diagrammatically illustrate var ions electrical configurations for the inductive element of FIGURES 1 and 2; and

FIGURE 10 illustrates a further embodiment capable of a broad band application.

DESCRIPTION OF PREFERRED EMBODIMENT Referring to the drawings and more particularly to FIGURES 1 and 2, there is illustrated an antenna system suitably mounted on a mast 10. The antenna system includes a. boom 12 which is disposed generally-in a hori- "ice zontal plane and is mechanically coupled to the mast 10 by a mast clamp arrangement 14. The boom 12 is typically formed of a lightweight, conducticve, weatherv resistant material sizch as, for example, aluminumv tubing. It will be understood that the boom 12 can likewise be fabricated from electrically insulating material such for example, a fiber glass reinforced plastic.

Spaced along the .length of, the boom 12, there is disposed a plurality of antenna dipole elements 16. The dipole elements 16 are preferably formed of unitary lengths of a light weight, weather resistant, electrically conductive material such as, for example, aluminum tubing. The spacing between and the length of each of the dipole elements 16 are so arranged as to obtain the desired directivity and response pattern of the antenna system under consideration. In a-unidirectional antenna system, the dipole elements 16 would normally be spaced at )\/4of the operating frequency of the antenna, and the dipole element 16' toward the'direction of the received signal wonld be resonant at a frequency slightly higher than the operating frequency and the dipole elements 16" at the end opposite the direction of the received signal would :be resonant at a frequency slightly lower than the operating frequency of the antenna system. The dipole element 16" would be resonant at the operating frequency.

Disposed in relatively close relation to and in a plane parallel to the antenna dipole elements 16, 16", and 16", there is disposed a resonant inductance element 18. The resonant inductance element 18 is typically mechanically secured to the bottom 12 by a pair of insulating brackets 20 and 22. The element 18 in the embodiment illustrated in FIGURES 1 and 2 is generally U-shaped and is approximately M4 in length from the closed end or base to the open ends. The element 18 is resonant at the operating frequency of the antenna system, and the limbs of the element are'parallel to one another and arranged symmetrically above the centers of the antenna elements and extend perpendicularly to the antenna elements and in a plane parallel to, and closely spaced from, the array.

The bracket 22 is provided with electrical terminals 24 and 26 which are adapted to be coupled to respective transmission line leads 28 and 30 of a transmission line 32 commonly referred to in the trade as twin-lead. The terminals 24 and 26 are in electrical contact with the resonant inductance element 1 8, and are positioned along the length thereof at a point where the impedance of the resonant inductance element 18 is equal to the impedance of the transmission line 32.

It will beunderstood that various numbers of dipole elements 16 may be employed and the number employed is tpicallyv a function of the gain of the antenna system.

Accordingly, as the number of ,such dipole elements is increased, the overall gain of the antenna is increased.

Now referring to FIGURE 1, the transmitted electromagnetic energy to be received by the antenna systemis propagated in a direction from element 16 towards element 16". The electromagnetic energy is normally polarized in a. horizontal plane which is the same plane as the plane of the dipole elements 16', 16", and 16 As the energy arrives at dipole element 16", a portion of it is absorbed. It will be understood that the element 16 is resonant at the frequency of the incoming signal. Since there is no resistance load terminating dipole element 16', i.e. the element is electrically continuous all of the absorbed energy will be returned to space in an in-phase relationship with the energy which is arriving at dipole element 16". Since there is no resistance load terminating dipole element 16, all of the absorbed energy will be returned to space in an in-phase relationship withthe incoming Wave front and with the energy arriving at dipole element 16". The dipole element 16" is resonant at a freas', I

I 3 quency slightly lowerrthan signal and therefore tends to reflect the energy back to the dipole element 16". At each of the dipole elements upon the reception of the incoming or received electromagnetic energy, there is caused a flow of current I, along the dipole elements 1 6', 16", 16" and an associated magnetic field H, as diagrammatically illustrated in FIGURE 3. Since all of the energy which arrives at the dipole elements is returned to space, a flow of current I is caused to pass between the dipole elements of the antenna, as diagrammatically illustrated in FIGURE 4. It will be observed that associated with the current I there is es.-

the frequency of the incoming tablished a magnetic field H The magnetic field H is matically illustrated in FIGURE 5. The magnetic field H 1 is coplanar with and coupled .to the magnetic field H associated with the current flow I which may be referred to as the free space current flow. 7

As will be apparent from the diagrammatic illustrations of FIGURES 3 and 4 the induced magnetic field H and the induced magnetic field H are oriented perpendicularly with respect to each other and, due to this fact, therewill be no coupling effect of the magnetic field H around the resonant inductance element 18 (FIGURE 5). Therefore, the coupling of element 18 is with respect to the magnetic fields H and H and in conductive electrical isolation from the dipole elements 16, 16", and 16"". Accordingly, the electrical characeteristics of the element 18 are likewise in electrical isolation from the dipole elements 16', 16", and 16" since there is no mutual conductive, inductive or capacitive coupling. Therefore, in designing an antenna system for receiving a given portion of the energy spectrum, the element 18 becomes an independent design parameter, i.e., it is dependent only on the wave length for which the array is designed.

In operation, the magnetic fields H and H induce the current I in the element 18. This current I is delivered to the transmission line 32 through the terminals 24 and 26 and the associated leads 28 and 30, respectively. The

transmission line 32 may be coupled to a suitable receiving device such as a television receiver, FM receiver, radio receiver, etc. Manifestly, although the above description has specifically been concerned with the antenna as an integral .part of a receiving system, it could likewise be satisfactorily employed as an integral part of a transmitting system.

The inductive element may be of configuration other than specifically' illustrated and described with reference to FIGURES 1 through 5. Other configurations would include the embodiments illustrated in FIGURES 6 coupling the element to a transmission line.

FIGURE 8 shows another embodiment of the inductively coupled element wherein the element 18" is in the for-m of an inductance-capacitance (L-C) circuit. Such an arrangement effectively reduces the overall physical length of the element from those shown in the other e'tnbodiments, but functions similarly.

v. .FIGURE.9. shows another. embodiment of the inductively coupled element wherein the element 18" has a coil L and an associated magnetic core.

There is illustrated in FIGURE 10 an antenna system employing the principles of the invention wherein the arrangeme'nt is capable of multiband application. More particularly, the arrangement is suitable for dual frequency application. A boom 12 is disposed to support a pair of spaced apart dipole elements, 40' resonant at a given frequency, and another pair of spaced apart dipole elements, 42' interdigitated between the elements, 40' and resonant at another frequency. 'An inductance drive element 44, similar to the earlier described elements 18, is suitably mounted to be inductively coupled to the magnetic field establishedby the dipole elements. The drive element 44 is typicallyequal in 'elfective length to one half the wave length of the lower frequency,-while. it would be. equal in length to the wave length of the-higher frequency of energy to be received. The arrangement has been found to function generally as described above with respect to FIGURES 1 to 5. l 1 I .While it is not certainthat the theory of the antennae illustrated and described above functions'exactly as explained, tests have borne out that'the system embodies excellent operating characteristics and is simpler in construction than heretofore known antenna systems. However, in order to more fully understand the operation of the antennasystems-described above, a review of the nature of electromagnetic.radiation will be of assistance.

A transverse electromagnetic traveling wave is a Wave in which. both the electric and magnetic fields are transverse to the direction of travel and'to each other. The velocity of propagation or speed of travel of such a wave is equal to the speed of light, and the frequency or wave length is the distance-between successive points of the same electrical phase in the wave. As a general rule, it may be stated that power may not betaken from a traveling wave unless it is first acted upon in such a manner as to create a standing wave. a t

Standing waves are established as a result of two waves of the same frequency traveling in opposite directions. Standing Waves in space result when an electromagnetic signal is reflected back toward'the signal source. Standing waves on ,a transmission line exist only when a signal is reflected back from a load. In order for an antenna element to radiate or receive power, it is necessary for a standing wave to exist on the antenna element. Power may :be taken from the standing wave because the wave is in effect standing still in one place rather than traveling at the speed of light, as in the case of the traveling wave, and the fields associated with the wave are alternately reversing their polarity at the speedof the wave frequency.

As a general rule it is necessary to create a standing wave before power may be taken from an incoming Wave front. With the above in mind, let us examine a Yagi type antenna array and observe what occurs as a traveling wave arrives along the axis of the array. For simplicity, we will now'not consider the standing Waves that exist on the dipole elements, but merely look at the waves that exist in space as a result of the parasitic elements. Since the parasitic elements of the Yagi array are not terminated in a load, all of the energy received by the elements will be returned to space. The incoming traveling wave may be represented by a sine wave As the sine wave arrives at the dipole director a voltage is impressed thereon. This energy is returned to space in the form of a traveling wave which may typically be represented by another sine wave. Sincethe dipole element is bidirectional, half of the power will travel to the right of the element, and the other half of the power will travel to the left of the element. The two waves will travel until they meet the reflector dipole where they are reflected back toward the incoming signal. The resultant of the incoming traveling wave signal and the reflected traveling wave will be a standing wave.

It will now be appreciated that we have satisfied the first requirement for taking the power from the traveling wave without considering the function of the dipole element; namely, a standing wave has been established. Since a standing wave exists in space in the antenna arrangement as explained above, a driven dipole element is not necessary to take power from the antenna array. A section of the transmission line arranged to provide mutual flux linkage with the magnetic field of the standing Wave will satisfy the requirements for the driven means and will provide advantages over a driven dipole element.

In lieu of a driven dipole, as in the case of an antenna operating in the electric field, a driven means is inductively coupled to the electromagnetic energy flowing between the associated dipole elements. Such an arrangement provides an inductive coupling between the driven means and magnetic field of the resultant standing wave. Any impedance from a very low to a very high value may be found at points along the driven means facilitating a very precise impedance match to the associated transmission line, thereby greatly simplifying the antenna design problems. With the foregoing description, it is considered that one skilled in the art may be appreciative 'of the functional aspects of the antenna systems illustrated and described herein.

In accordance with the provisions of the patent statutes, I have explained the principles and mode of operation of my invention, and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

What I claim is:

1. An antenna array comprising:

a support; i

at least three spaced-apart, electrically continuous antenna elements mounted on said support,

said antenna elements being parallel to one another, within the same plane, and spaced apart substantially )\/4 of the operating frequency of the antenna array; an inductance element substantially resonant at the operating frequency of the antenna array,

said inductance element being generally U-shaped with parallel limbs perpendicular to said antenna elements and disposed symmetrically about the center one of said antenna elements in a plane parallel to and closely spaced therefrom;

lead-in coupling means on said inductance element;

and

transmission line means coupled to said lead-in coupling means for delivering a signal to a receiver,

said lead-in coupling means being located at a position on said inductance element where the impedance of the inductance element matches the characteristic impedance of the transmission line means.

2. An antenna array comprising:

a support;

at least three spaced-apart, electrically-continuous antenna elements mounted on said support,

said antenna elements being parallel to one another, within the same plane, and spaced apart substantially N4 of the operating frequency of the antenna array; an inductance element substantially resonant at the operating frequency of the antenna array,

said inductance element being in the form of an elongated loop with parallel longitudinal limbs perpendicular to said antenna elements and disposed symmetrically about the center one of said antenna elements in a plane parallel to and closely spaced therefrom; capacitive lead-in coupling means on said inductance element; and transmission line means coupled to said capacitive lead-in coupling means for delivering a signal to a receiver,

said capacitive lead-in coupling means being located at a position on said inductance element where the impedance of the inductance element matches the characteristic impedance of said transmission line means.

References Cited UNITED STATES PATENTS 2,212,214 8/ 1940 Smith 343-862 X 2,397,543 4/1946 Fuchs 333-9 1,914,886 6/1933 Franklin 343-730 X 1,933,669 11/1933 Gilman 333-9 X 2,031,065 2/1936 Posthumus et al. 343-853 X 2,066,900 1/1937 Posthumus et al. 343-814 X 2,128,400 8 /1938 Carter 333-9 X 2,404,093 7/1946 Roberts 343-725 X 2,963,703 12/1960 Sletten 343-811 X FOREIGN PATENTS 221,23 5 4/ 1959 Australia.

OTHER REFERENCES Ses'hadri et ial.: A Dipole Coupled Electromagnetically to .a Two-Wire Transmission Line, IRE Transactions on Antennas and Propagation, vol. AP-7, 1959, pp. 386-392.

Noll et al.:-Television and FM Antenna Guide, chapter 2, sec. 32, Line Sections As Tuning Stubs, pp. 49- 52.

King et al.: Transmission Lines, Antennas and Wave Guides, cha ter I, sec. 40, Single Stub Impedance Matching, pp. 45-48.

Chen and King: Dipole Antennas Coupled Electromagnetically To a Two-Wire Transmission Line, IRE Trans. on Antennas and Propagation, September 1961, pp. 425-432.

Forbes: An Endfire Array Continuously Proximity- Coupled, December 1959, pp. 1-18. Also found in AP-8, p. 518.

ELI LIEBERMAN, Primary Examiner W. H. PUNTER, Assistant Examiner US. 01. X.R. 343-856, 861 

